Differential Phase - φDP
EM waves travel slower
through water than through air. The difference in returned phase
between the H and V pulses is caused by differences in moisture
content. A horizontally polarized wave will have a larger phase shift
and will propagate more slowly if the hydrometeors are horizontally
oriented compared to a vertically polarized wave (and vice-versa). φDP is independent of calibration, immune to attenuation, and dependent on concentration. The change in φDP with range is strongly related to precipitation rate, liquid water content, and ice water content. High range gradients of φDP
are indicative of high moisture content. Abrupt changes are indicative
of large particles (e.g. hail, wet snow), ground clutter, or biological
targets.